Hitherto known circular looms comprise a plurality of partial heald shafts, which are arranged circularly around the circular reed of the loom, and each has a plurality of inner and outer healds for the guidance of a part of the two systems of warp yarn distributed all around the arrays of healds, which, for the formation of the weaving shed or travelling shed, are given by the main shaft, an opposing up-and-down alternating motion. The weaving shuttles circulated in the circular reed by the main shaft carry the weft threads which are unwound from the respective bobbins carried by the shuttles continuously into the travelling shed. The tubular fabric thus manufactured is then drawn off and spread as a flat tubular fabric.
It is essential that the weft threads wound off the circulating shuttles be meticulously supervised in order to switch off the loom immediately, so as to avoid weaving faults, in the case of a weft thread failure, owing to weft thread breakage or depletion of the weft thread package, for example.
Hitherto-known arrangements of this kind employ for this purpose photo-visual signal transmitters or work with loop contact. Light barrier means as well as loop contacts are unable to satisfy today's requirements, in particular with regard to the substantial increase in the rotational speed of the weaving shuttles. Light barrier means have, moreover, always been susceptible to the effect of outside light, quickly become dusty and do not permit the manufacture of reflex bands or tapes owing to their becoming "blind". Loop contact means are, on the other hand, of only very limited use on today's high-performance looms.